1. Field of the Invention
The present invention relates to an elevator having a compensating cable and, more particularly, to a compensating cable having specific flexibility characteristics selected such that the compensating cable is capable of attaching to an elevator car at a centerline such that the elevator car, and a load carried thereby, is more effectively balanced when the elevator is in operation.
2. Description of Related Art
An elevator car installation typically uses a compensating cable arrangement, as will be appreciated by one skilled in the art. Such a compensating cable is generally flexible and can be hung at very long lengths in an elevator hoistway. Because the compensating cable is attached to the elevator car and a counterweight, which move vertically and opposite each other, the cable defines an arcuate loop at the lower portion of the elevator hoistway that connects a first portion attached to the elevator car and a second portion attached to the adjacent counterweight. In conventional compensating cable arrangements, the arcuate loop of the cable defines a relatively small diameter such that the first portion of the cable attaches to the elevator car at an off-center position (often at a position nearest the counterweight in the hoistway) on a lower portion of the elevator car. Thus, in conventional elevator systems, the weight of the compensating cable produces a substantial off-center force on the lower portion of the elevator car, especially while the elevator car is located at higher locations within the hoistway (where the length and weight of the compensating cable is at a maximum).
In conventional elevator systems, the unbalanced weight force generated by the off-center attachment of the compensating cable to the elevator car is, in some systems, balanced by a car counterweight that may be attached to the side of the elevator car opposite the attachment point of the compensating cable. In addition, in other conventional systems, additional compensating cables may also be attached to the lower portion of the elevator car such that the overall force generated by the weight of the various compensating cables is generally balanced. While these systems are somewhat helpful in attaining and maintaining balance in the elevator car during its operation, these systems may also produce other problems, such as the need for a specialized damping or guide system to ensure that multiple compensating cables track properly and remain tangle-free as they travel through the hoistway during the operation of the elevator system. In addition, car counterweight systems in conventional elevator systems may not be fully effective for balancing the elevator car as it travels to the highest floors in the hoistway. For example, in conventional elevator systems, the weight of the compensating cable when the elevator is located at higher positions within the hoistway may overcome a balancing weight force provided by the car counterweight attached to the elevator car. Thus, when the elevator car is hoisted to the upper levels of the hoistway, the weight of the compensating cable may cause the elevator car to tilt slightly towards the counterweight. In a similar manner, when the elevator car is lowered to the lower portions of the hoistway, the weight of a car counterweight (in comparison to the relatively light/short portion of the compensating cable) may cause the elevator car to tilt slightly away from the counterweight. In all of the above-mentioned situations, the imbalances encountered by the elevator system will tend to cause more rapid wear on the components of the elevator system and/or require that the elevator system be serviced and balanced more often. Ultimately, these conditions adversely affect elevator ride quality.
Thus, there exists a need for a compensating cable that may be attached to an elevator car so as to reduce and/or minimize imbalances in an elevator system. Furthermore, there exits a need for a compensating cable having mechanical characteristics supporting an imbalance-minimizing configuration. There also exists a need for an elevator system including a compensating cable that provides improved balance to an elevator car and associated elevator system components so as to reduce costs, decrease wear, and facilitate the extension of the required maintenance intervals for the elevator system.